A technology of capturing videos of surroundings of a vehicle with cameras that are arranged around the vehicle and displaying, on a monitor, a bird's-eye view video obtained by performing viewpoint conversion processing on the captured videos and synthesizing the captured videos is known (see, for example, Japanese Laid-open Patent Publication No. 2007-318460, Japanese Laid-open Patent Publication No. 2007-266930 and Japanese Laid-open Patent Publication No. 2015-106777). Japanese Laid-open Patent Publication No. 2007-318460 discloses a technology of, when a change in an inclination of a road surface is detected, correcting a distortion occurring in a video of a bird's-eye view from above. Japanese Laid-open Patent Publication No. 2007-266930 and Japanese Laid-open Patent Publication No. 2015-106777 disclose technologies of sensing an inclination of cameras, correcting the inclination of the cameras, and performing synthesizing.
In a case where a point right above a vehicle is set for a virtual viewpoint, when the road surface is inclined and thus the vehicle is also inclined, the virtual viewpoint is also inclined to a vertical direction together with the vehicle. In a generated bird's-eye view video, signs and structures built along the vertical direction are displayed as being inclined. For this reason, when a driver tries to check the surroundings of his/her vehicle by using the bird's-eye view video, the driver may feel something odd.